Probabilistic Heavy Snow and Icing Discussion
NWS Weather Prediction Center College Park MD
320 PM EDT Sun Oct 11 2020

Valid 00Z Mon Oct 12 2020 - 00Z Thu Oct 15 2020

Days 1-3...

...Pacific Northwest to the Northern Rockies...
A reinforcing shortwave trough in a strengthening westerly jet
aimed right as Vancouver Island/northern WA will reach Vancouver
Island/the Olympic peninsula this evening and push across the
northern Rockies to central MT Monday. This strong and deep zonal
flow will persist across the northwest CONUS into midweek, until
the next embedded shortwave trough reaches Vancouver
Island/northern WA late Tuesday (and MT Tuesday night). This will
make for two distinct waves of precip with mountain snows for the
Cascades and northern Rockies tonight into Monday and again late
Monday night through Tuesday night.

Snow levels of 7000 to 9000ft are ahead of the shortwave that
reaches the coast this evening and quickly drop to around 5000ft
late tonight through Monday (as precip tapers off) then rise again
to 7000 to 9000ft Monday night/Tuesday ahead of the next wave.
Therefore, heavy snowfall tonight and Monday night/Tuesday will be
limited to the higher WA Cascades and the Bitterroot Range and
northern Rockies of eastern ID and western MT, along with the
Tetons, Sawtooth, and Wind River ranges in northwest WY.
Probabilities of at least 6 inches in 24 hrs are highest over
these higher ranges -- exceeding 50% over the highest peaks. By
day 2.5 (12Z Tue-12Z Wed), 24hr probs of 6+ inches will be
confined to the northern WA Cascades and far northern Rockies in
northwest MT.


The probability of significant icing is less than 10 percent.

Jackson